Halftone image signal processing apparatus in which pixels of a dither threshold pattern are each divided into an operator-selected number of micropixels

ABSTRACT

A halftone image recording apparatus includes means for recording an image on a recording medium, inputting an image signal representative of an image which includes a plurality of density levels, generating a plurality of pulsed periodic signals having different widths of one period of the image signal, selecting at least one periodic signal with a preselected pulse width among a plurality of the periodic signals, combining the selected periodic signal with the image signal, and applying the combined signal to the recording means.

This application is a continuation of application Ser. No. 07/063,741filed June 18, 1987, now abandoned, which is a continuation ofapplication Ser. No. 06/585,603 filed Mar. 2, 1984, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image processing apparatus forprocessing images by applying a digital processing technique thereto.

2. Description of the Prior Art

In the prior art, there is known a color copier wherein an originalimage is subjected to color separation into three colors using a colorseparation filter. The original is scanned for each color separation, alatent image is formed on a photosensitive body by a color-separatedluminous image to be developed with a complimentary color developer, anda multi-color superposition is carried out to reproduce a color image.

As for these kinds of color copies, since color balance is necessary forthe reproduction of color images, half-tone representation and the likehave been implemented by utilizing analog characteristics ofelectrostatic photography, adjustment for the image exposure amount andelectric charging conditions for the photosensitive body and so on aremore complicated. Also, the variation in image quality is largely due tochanges in the environment, as corona charging, photosensitive elementsand the like would often suffer directly from the effects of temperatureand humidity.

Further, since the process, from reading-out of the original image toformation of a latent image, has been put into practice through alltwo-dimensional optical systems, it was impossible to process the imageat the separate points thereof.

SUMMARY OF THE INVENTION

In view of the aforementioned problems, the present invention has beenimplemented, and it is an object of the present invention to provide animproved image processing apparatus capable of reproducing ahigh-quality image.

Another object of the present invention is to provide an imageprocessing apparatus capable of correcting a gradient of color imagedata.

A further object of the present invention is to provide an imageprocessing apparatus wherein digital processing is carried out in realtime by means of some memory means.

Yet another object of the present invention is to provide an imageprocessing apparatus capable of implementing color image processing athigh speed.

Another object of the present invention is to provide an imagereproduction apparatus which is excellent in half-tone reproduction offull colors.

Another object of the present invention is to provide an improveddigital processing color copier.

Another object of the present invention is to provide an imageprocessing apparatus that makes variable the parameters of digital imageprocessing.

Another object of this invention is to provide an image processingapparatus in which the number of gradations can be selected inaccordance with reproduced images, with the number of gradations orthreshold matrices being variable.

Another object of this invention is to provide an image processingapparatus capable of reducing moire and other factors through ditherprocessing by means of a dither matrix which differs according tocolors.

Another object of this invention is to provide an image processingapparatus whose constitution is simplified through multi-gradation ofcolor data by means of uniform multi-value processing techniques.

Another object of this invention is to provide an image processingapparatus wherein images can be reproduced at higher speeds byeliminating the under color in real time.

Another object of this invention is to provide an image processingapparatus in which the quality of images can be upgraded because thecorrection value for eliminating under colors is different from the peakvalue of color data.

Another object of this invention is to provide an image processingapparatus capable of reproducing high-quality color images by correctingthe characteristics of color separation with a filter.

Detailed explanation concerning the foregoing descriptions and otherobjects of this invention will be given hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a color copier in accordance withthe present invention;

FIG. 2-1 illustrates the spectroscopic characteristics of a halide lampand the spectral sensitivity characteristics of a CCD;

FIG. 2-2 illustrates the spectral sensitivity characteristics of a CCDthrough a color separating prism and a multi-layer film filter;

FIG. 2-3 illustrates the spectroscopic characteristics of a colorseparating prism;

FIG. 2-4 illustrates the spectroscopic characteristics of each colorfilter;

FIG. 3-1 is a block circuit diagram showing a main unit controller;

FIG. 3-2 illustrates an operational part of said main unit controller;

FIG. 3-3 illustrates an operational part of a sub-control unit;

FIG. 3-4 illustrates a timing chart showing an operative timing of eachportion of said color copier;

FIG. 3-5 illustrates a schematic configuration of a sequence clockgenerator;

FIG. 4 is a block diagram showing a schematic configuration forprocessing the color images;

FIG. 5-1 is a block circuit diagram showing the construction of asynchronous control circuit;

FIG. 5-2 illustrates a timing chart of the signals in said synchronouscontrol circuit;

FIG. 6-1 illustrates the construction of a CCD;

FIG. 6-2 is a block diagram of a CCD driver;

FIG. 7-1 illustrates a distribution of quantity of light on the surfaceof a CCD:

FIG. 7-2 is a block circuit diagram showing a shading correctioncircuit;

FIG. 8-1 is a block circuit diagram showing Υ correction circuit;

FIG. 8-2 is a view showing the relationship among an originalconcentration, characteristics of a CCD and an image processing unit,and the concentration of reproduced images;

FIG. 9-1 illustrates the spectral reflection characteristics for atoner;

FIG. 9-2 is a block circuit diagram showing a masking processingcircuit;

FIG. 10-1 is a block circuit diagram showing a masking processingcircuit and a UCR processing circuit;

FIG. 10-2 illustrates any condition of the signals outputted from alatch circuit in response to the magnitude of image data;

FIG. 10-3 illustrates a UCR processing;

FIGS. llA and llB illustrate the principle of multi-gradient processing;

FIG. 12-1 is a block circuit diagram showing a dither processingcircuit;

FIG. 12-2 is a block circuit diagram showing multivaluation processingcircuit; and

FIG. 13 illustrates a timing chart of signals in the circuit shown inFIG. 12-1 and FIG. 12-2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following descriptions, given in detail, are concerned with theillustrative embodiments of this invention being put into practice, isshown in the drawings.

FIG. 1 shows a sectional view of a copier to which this invention isapplied.

The original 1 is placed on the transparent plate of the script stand 2and pressed by the script cover 3 from above. The light focused by thehalogen lamps 5 and 6 (both illuminate the original) and reflectorshades 7 and 8 irradiate the original and the reflected light isradiated on the movable reflex mirrors 9 and 10. This reflected lightthen goes over to the color separating prism 12 after passing throughthe lens 11-1 and infrared cut filter 11-2. At the color separatingprism 12, the light is separated into three spectral components eachhaving a different wave length i.e. blue (B), green (G), and red (R).The three separated lights (B, G and R) undergo regulation of lightintensity and correction of separation characteristics by means of bluefilter 13, green filter 15, and red filter 17, respectively, and thenthe entire light is received by the solid image pickup elements (CCD)210, 220 and 230.

The image reflected from the original 1 is formed on the solid imagepickup elements (CCD) 210, 220 and 230 in the same way as mentionedabove, at half the moving speed of the movable reflex mirror 9 whosemotion is integrated with the halogen lamps 5 and 6. This occurs afterthe image goes through the lens 11 1, infrared cut filter 11-2, andcolor separating prism 12, with a constant length optical path beingmaintained by the reflex mirror 10 which moves in the same direction.The output of each solid pickup element undergoes digital signalizationat the CCD light receiving unit 200 (see FIG. 4, which will be mentionedlater) of each CCD. The image processing unit 100 processes the imageand releases a laser beam which is modulated by an image signal from thelaser modulation unit 300 to a polygon mirror 22, and then irradiates aphotosensitive drum 24. The polygon mirror 22 is revolving at a regularspeed which is controlled by the scanner motor 23, and the laser beam isbeing vertically scanned in the same revolving direction as thephotosensitive drum 24.

The photosensor 64, which is set up before the point where the laserstarts scanning the photosensitive drum 24, produces the horizontalsynchronizing signal BD of the laser caused by the passage of laserbeams. After being evenly charge-erased by the charge erasure electrode63 and charge erasure lamp 71, the photosensitive drum 24 becomesuniformly negatively charged by the minus charger 25 which is connectedto the high voltage generator 77. When the laser beam (which ismodulated by the image signal) contacts the photosensitive drum 24(which is uniformly negatively charged), the electric charge of thephotosensitive drum 24 flows to ground and is eliminated through theoptical conduction of electricity. The laser shall be turned on in thehigh density area and turned off in the low-density area of theoriginal. Under these conditions, the electric potential on the surfaceof the photosensitive body ranges from -100 V to -50 V in thehigh-density area and around -600 V in the low density area of theoriginal placed on the photosensitive drum 24. An electrostatic latentimage is formed in this way depending on the light and shade of theoriginal.

This electrostatic latent image is then developed by the yellowdeveloper (Y) 36, magenta developer (M) 37, cyan developer (C) 38, orblack developer (BK) 39, which is selected by the signal from the mainunit controller 400. A toner picture is then formed on the surface ofthe photosensitive drum 24. In that instance, a voltage is applied fromthe developing bias generator 84 so that the electric potential of thedeveloping sleeves 85, 86, 87 and 88, which are within the developer ofeach color, should be kept between -300 V and -400 V.

The toner within the developers is stirred and negatively charged sothat it adheres to the spot where the surface potential of thephotosensitive drum 24 exceeds the developing bias potential. A tonerpicture is thus formed in conformity with the original. Then, by meansof the high voltage generator 77 and lamp 40, which is designed to erasethe drum surface potential, the unnecessary electric charge remaining onthe photosensitive drum 24 is eliminated by the negatively charged postelectrode 41, thereby equalizing the surface potential of thephotosensitive drum 24.

The transfer paper, on the other hand, which is stored in either of thecassettes 42 or 43 (cassette selection is made via the operation board72), is supplied through paper feeding action performed by either thepaper feed roller 46 or 47. Oblique movement of the paper is correctedby the first resist roller 49 or 50, and the paper is conveyed within aprescribed duration of time by the convey roller 51 and second resistroller 52. The margin of the transfer paper is firmly retained by thegripper 57 of the transfer drum 53, around which the transfer paper iselectrostatically wrapped.

The toner picture formed on the photosensitive drum 24 is transcribedonto the transfer paper by the transfer electrode 54 at the point whereit comes in contact with the transfer drum 53. Transfer of the tonerpicture onto the transfer paper is repeated as many times as defined bythe copying color mode being selected. Upon completion of the transferof all toner pictures, paper charge erasure is performed by the chargeerasure electrode 55 for which high voltage is supplied from the highvoltage generator 77. After the transfer is performed as many times asprescribed, the transfer paper is peeled from the transfer drum 53 bymeans of a split nail 90 and directed to the fixing device 60 afterbeing drawn onto the convey belt 59 by means of the convey fan 58.

The residual electric charge remaining on the photosensitive drum 24 isfurther erased by the pre-cleaner charge eraser 61, and the residualtoner remaining on the photosensitive drum 24 is eliminated by thecleaning blade 89 located in the cleaner unit 62. Further, the electriccharge on the photosensitive drum 24 is eliminated by the pre-AC chargeeraser 63 and charge erasure lamp 71. The process then continues to thenext cycle.

Heat generated by the lighting system is discharged by the cooling fans19 and 20 of the optical system.

Now, the case of full-color mode will be explained, with the operationsequence being categorized into four colors (Y, M, C and BK). Prior tothe scanning of original 1, the white calibration plate 4 is scannedevery time. This is intended to read the white calibration plate 4 inthe image processing unit 100 of one scanning line for shadingcorrection purposes, which will be mentioned later. Then, as originalscanning continues, the three-color (B, G and R) image is read outsimultaneously at CCD 210, 220 and 230. The quantity of Y, M, C (whichare the complementary colors of B, G, R, respectively) and BK of blackplate is calculated at the image processing unit 100 and the process ofcolor modification and other steps are implemented.

Original scanning is performed four times. The signal of yellow (Y)component, calculated at the image processing unit 100, undergoes lasermodulation at the first scanning, thereby forming a latent image on thephotosensitive drum 24. This latent image is developed by the yellowdeveloper 36 and transferred to the paper which is wrapped around thetransfer drum 53. Other images are transferred to the paper likewise,i.e., magenta (M) by the magenta developer 37 at the second scanning,cyan (C) by the cyan developer 38 at the third scanning, and black (BK)by the black developer 39 at the fourth scanning. These images are fixedby the fixing device 60, and then image recording in the full-color modeis completed.

As illustrated in FIG. 2-1, the spectral energy distribution of ahalogen lamp for original exposure features high optical output in thelong wave lengths (red area) and low optical output in the short wavelengths (blue area). Wavelengths ranging between 500 and 600 nm (greenarea) features high spectral sensitivity in CCD, as shown in FIG. 2-1.The light reflected from the original, therefore, varies in accordancewith the spectral characteristics of the halogen lamp after encounteringthe output from the color separating prism 12, as illustrated in FIG.2-2.

The spectral characteristics of the color separating prism 12 areinferior, as is obvious from FIG. 2-3. Therefore, through the multi-filminterference filter, which features a spectral transmission factor asshown in FIG. 2-4, an optical image from color separation withoutunnecessary wavelength components may be produced as shown by theDICHROMATIC OUTPUT dashed lines in FIG. 2-2. Also, the spectraltransmission factor may be changed by overlapping a plurality of filtersfor each color, thereby correcting the unbalanced output as shown by theAFTER CORRECTION dashed lines in FIG. 2-2.

A block diagram of the main unit controller 400 (FIG. 4) is given inFIG. 3-1. The main control unit 422 and the sub control unit 421, whichconstitute the operating unit, are handled by a mechanical operator. Themain control unit 422, as illustrated in FIG. 3-2, corresponds to theoperating board 72 shown in FIG. 1. Number 72-9 indicates a copy buttonto start the copying action, 72-19 a numerical value input key system toset the number of copies, 72-16 and 72-17 a cassette selection key toselect the lower or upper cassette (42 and 43, respectively, in FIG. 1),and 72-2 to 72-8 a color mode selection key to select the color copymode.

For example, the 4 Full mode selected by the 72-2 key is the mode whereoriginal exposure scanning is repeated 4 times and the development bytoners, Y, M and C, is performed in accordance with the exposed imagewhose color is separated into B, G and R for each scan. At the fourthscan, development by toner BK is performed corresponding to the BKcomponent of the original, and a copy of the full color image isproduced by superposing all 4-color images. Likewise, copies areproduced by toners Y, M and C for each of the three exposure scans inthe 3 Full mode; by BK and M for two exposure scans in the BK+M mode;and by single color toner image for one exposure scan in the BK, Y, M, Cmode.

Reference numeral 72 23 indicates a 7 segment LED to show the number ofcopies being set, 72-18 a 7 segment LED to show the number of copiesbeing counted, 72-15 the indicator which lights when there is no feedingtoner in the hopper (not illustrated) as determined by a detector (notillustrated), 72-14 an indicator which is energized when a jam isdetected by a jam detector equipped in the paper conveying channel ofthis apparatus, 72-20 the indicator which is energized when no paper inthe selected cassette is detected by a detector (not illustrated), and72-1 a wait indicator which lights when the surface temperature of thefixing roller in the thermal pressure fixing device 60 does not reach aprescribed degree. Copying action will not start if any or all of theindicators 72-15, 72-14, 72-20 and 72-1 are turned on.

Indicator 72-21 lights when copy papers (selected by the paper sizeindicator) within a cassette are of A3 size. Indicator 72-22 lights whencopy papers are of A4 size. Selector 72-12 works by means of the copydensity control lever so that the lighting voltage of halogen lamps 5and 6 decreases when the lever is shifted toward setting 1 and increaseswhen it is shifted toward setting 8.

The sub control unit 421 now will be explained with reference to FIG.3-3. Reference numerals 421-14 to 421-16 are the switches connected tothe Y correction circuit 140 (mentioned later in connection with FIG. 4)which corrects the gradient features of read out data against the 8-bitpicture element data read out at CCD and quantized by an A/D converter.These are made up of rotary digital code switches which give rise toeach digital code. As explained later, these switches are connected sothat data conversion memory elements with required Υ characteristics canbe selected from a plurality of memory elements accommodated in the dataconversion table within the Υ correction circuit.

Reference numerals 421-5 to 421-13 indicate the switches to be used formasking processing. At the masking processing circuit 150 (mentionedlater in connection with FIG. 4), the coefficients ai, bi, and ci (i=1,2 and 3) applying to the following conversion equations shall beestablished against the input image data Yi (yellow), Mi (magenta) andCi (cyan). As in the case of switches 421-14 to 421-16 above, these aremade up of rotary digital code switches which generate the digital codesranging from 0 to 16.

Data conversion equations for masking processing are as given below:

    Yo=a.sub.1 Yi-b.sub.1 Mi-c.sub.1 Ci

    Mo=-a.sub.2 Yi+b.sub.2 Mi-c.sub.2 Ci

    Co=-a.sub.3 Yi-b.sub.3 Mi+c.sub.3 Ci

Reference numerals 421-1 to 421-4 represent the rotary digital codeswitches that provide coefficients of correction for the data Y, M, Cand BK at the UCR processing circuit 160 (mentioned later in connectionwith FIG. 4). Reference numerals 421-20 to 421-23 constitute the volumecontrols connected individually to the high voltage generator 77. Thesevolume controls control the current flowing into the charger 25 by whichthe photosensitive drum is equally charged with negative electricity.The pictorial light and shade of each color is adjustable and colorbalance is changeable by means of this volume. Reference numeral 421 24is the switch for selecting gradient characteristics at the time ofmulti-value dither processing, as explained later.

Again referring to FIG. 3-1, reference numeral 411-65 represents thesequence controller that controls all loads in the entire apparatus. Theload shown in the timing chart of FIG. 3-4, including the drive motor ofphotosensitive drum 24, charge eraser, exposure lamp, etc., is drivenfrom the sequence controller through I/O port 419 to load drive circuit420 at a prescribed length of time conforming to the sequence controltable in ROM 423. The marks L₁, L₂ . . . L_(N) in FIG. 3-1 stand for thevalue of each load, but the driving method of each load, includingsolenoid, motor, and lamp, as well as the sequence control method basedon ROM, are all well known, and therefore the explanation concerningthese is omitted here. The main control unit 422 and the sub-controlunit 421 correspond to the operating section respectively. But thedriving load involves the key, lamp, LED, etc., and the drive of, orinput in, these devices is implemented by the key and display controller412.

The driving of the LED and lamp, scanning of keys, and method of input,for example, are performed in a well-known way, and therefore detailedexplanation is omitted. The progress of the sequence is subject to thetiming chart given in FIG. 3-4. This is an example of a timing chartthat brings a full color image sequence by superposing three differentcolors (Y, M and C). In this apparatus it is necessary to turn 5 timesthe photosensi tive drum 24 and 10 times the transfer drum 53 in orderto achieve a full color image in the above three colors. The diameter ofthe photosensitive drum 24 and transfer drum 53 therefore features aratio of 2 to 1.

The implementation of this sequence is subject to the revolution of thephotosensitive drum 24 and transfer drum 53. As illustrated in FIG. 3-5,the sequence is produced, as the photosensitive drum 24 revolves, bymeans of the clock board 24 7 which is driven by the gear 24-9 (drivenby the driving shaft 24 10 of the photosensitive drum 24) as well as bymeans of the sequence clock generator which is composed of thephotointerrupter 24-8. The sequence progresses in response to the drumclock C, with the clock counting 400 per revolution of the transferdrum. The on off control of the load is therefore performed on the basisof counting at the home position (hereinafter referred to as "HP") ofthe transfer drum 53.

In the timing chart of FIG. 3-4, the numerals indicating the operationaland non-operational timing represent each clock-counting value, with theclock number at the transfer drum HP being set at 0. For example, theexposure lamps 5, 6 go on at clock count 120 in the third revolution ofthe transfer drum, at 120 in the fifth revolution, and at 120 in theseventh revolution, respectively. It goes off at clock count 118 in thefourth revolution, at 118 in the sixth revolution, and at 118 in theeighth revolution, respectively.

Given the timing chart of FIG. 3-4, the operational steps of the presentimage processing apparatus are outlined as follows according to itsstructural drawing shown in FIG. 1. When the switch on of copy button72-9 is sensed by the key and display controller 412, the sequencecontroller 411-65 starts the copy sequence and begins to drive thephotosensitive drum 24, transfer drum 53, first resist rollers, i.e.,either 49 or 50, convey roller 51 and second resist roller 52. After onerevolution of the photosensitive drum 24, the charge on the drum surfaceis erased by the pre charge erasers 61 and 63, charge erasure lamp 71,and other devices, thereby being electrostatically equalized.

The original 1 is placed on the platen glass stand 2, and exposurescanning starts when the halogen lamps 5 and 6 (for original exposure)go on at the 120th clock pulse in the third revolution of the transferdrum 53. The image reflected from the original is reflected on themirrors 9 and 10, and the light is condensed by the lens 11-1 to form animage on the surface of CCD 210, 220 and 230. It then goes into thecolor separating prism 12, and the optical image reflected from theoriginal also goes into CCD 210, 220 and 230 after being separated intothe colors B, G and R. The optical image separated by colors, which isthe counterpart of the original whose light is received at each CCD,first undergoes photoelectric conversion and then data processing inreal time, which is performed by the image processing unit 100(mentioned later). Then, as explained before, the photosensitive drum 24is exposed successively in the order of Y, M and C by the laser light lwhich is modulated by the image data above, and a latent imagecorresponding to the original is now formed on the surface of thephotosensitive drum 24.

In the timing chart of FIG. 3-4, the latent image, formed on thephotosensitive drum 24 in response to the first exposure scan, begins tooperate at the 254th clock in the third revolution of the transfer drum53, and is developed by the Y (yellow) developer 36 which ceases tooperate at the 293rd clock in the fourth revolution. It then startsaction at the 196th clock in the same revolution, and by means of thetransfer charger 54, which stops action at the 196th clock in the nextrevolution, a yellow toner image corresponding to the yellow componentof the original is transferred to the paper which is wrapped around thetransfer drum 53.

Likewise, a magenta toner image corresponding to the magenta componentof the original is transferred to the paper in the fifth, sixth, andseventh revolutions of the transfer drum 53. A cyan toner imagecorresponding to the cyan component of the original is transferred tothe paper in the seventh, eighth, and ninth revolutions. All these tonerimages are multi transferred at a prescribed timing so that the marginof developed images Y, M and C should coincide.

The optical image reflected from the original goes into CCD 210, 220 and230 at the color separating prism 12 after being separated into threecolor components B, G and R. For color correction, however, the signalsG and R are used at the time of image reading to form a yellow tonerimage, the signals B and R are used at the time of image reading to forma magenta toner image, and the signals B and G are used at the time ofimage reading to form a cyan toner image. These processings areconducted successively in the order of Y, M and C.

At the 225th clock pulse in the third revolution of the transfer drumwhere the first exposure scan is performed, the paper feed rollers 46and 47 begin to work in the upper and lower cassettes, respectively, tofeed transfer papers from either of the cassettes 42 or 43 selected atthe operation unit. The transfer papers fed from either cassette 42 or43 are conveyed by the either of the first resist rollers 49 or 50, andtheir oblique movement is corrected by the convey roller 51. At thesecond resist roller 52, a prescribed timing is established so that thetransfer papers are held firmly by the gripper 57 of the transfer drum53. After their margin is fixed by the gripper 57, the transfer papersare wrapped around the transfer drum 53 to accomplish the multipletransfer of toner images, as mentioned before.

Upon completion of the multiple transfer, the transfer papers are drawnoff from the transfer drum 53 by the split nail 90 and directed by theconvey belt 59 to the fixing device 60, where they are fixed by thermalpressure and discharged. The operational timing pertaining to each ofthe load discussed above is as shown in the timing chart of FIG. 3-4.

FIG. 4 shows a block diagram outlining the composition of this inventionfocusing on the image processing unit 100. The image processing unit 100constitutes the part for computing a proper quantity of the signalsY(yellow), M(magenta), C(cyan), and BK(black), all of which arenecessary for printing based on the 3-color image signals read out atthe CCD light-receiving unit 200. These colors have their respectiveoutput for the laser modulation unit 300.

In order to produce a color picture by means of this apparatus, it isnecessary to scan the original 4 times with the CCD light-receiving unit200 in the case of 4-color (Y, M, C and BK) printing and 3 times in thecase of 3-color (Y, M and C) printing. That is, multi-color printingrequires superposed original scanning.

The image processing unit 100 is composed of the following circuitblocks. Block 130 makes up a shading correction circuit that correctsthe optically unequal illumination of the image signals read from theCCD light receiving unit 200, where correction is performed individuallyat every scan for the color separated signals Y, M and C. Block 140 is aΥ correction circuit that corrects the gradient characteristics of eachcolor signal in conformity with the masking and UCR corrections. Block150 is a masking processing circuit that calculates an appropriatequantity of Y, M and C needed for printing. Block 160 is a UCRprocessing circuit that calculates an appropriate quantity of BK basedon Y, M and C for the purpose of preparing an ink plate. Block 170 is adither processing circuit that makes a 2-value half-tone picture basedon the dither method. Block 180 is a multi-value processing circuit thatenhances the gradient characteristics of a half-tone picture by furthermodulating the pulse width of the 2-value image signal available fromthe dither processing circuit 170. The image processing unit 100 is madeup of these processing circuits and synchronous control circuit 190which synchronizingly controls these circuits.

The CCD light-receiving unit 200 is the section that separates anoptical image into three colors (B, G and R) by means of the colorseparating prism 12 and transforms them into electric signals. The threedifferent lights B, G and R undergo photoelectric conversion byCCDB-210, CCDG-220 and CCDR-230, respectively. The photoelectricallyconverted signals B, G and R undergo 8-bit digitalization by CCD driversB-240, G-250 and R-260, respectively. They are further converted intosignals Y, M and C which are the complementary colors of B, G and R.

The 8-bit digitalized signals Y, M and C shall be called VIDEO-Y,VIDEO-M and VIDEO-C respectively. By way of the signal lines 271, 272and 273 respectively, VIDEOs Y, M and C are connected with the shadingcorrection circuit 130, which performs shading correction as alreadyexplained. The shading corrected signals Y, M and C, i.e., VIDEOs Y, Mand C, are fed into the Υ correction circuit 140 via the signal lines105, 106 and 107 respectively. In the Υ correction circuit 140, thegradient characteristics are changed into those suited for colormodification.

VIDEOs Y, M and C are converted into 6-bit signals in order to simplifythe following processing steps. The 6-bit VIDEOs Y, M and C which haveundergone Υ correction are sent to the masking processing circuit 150 byway of the signal lines 108, 109 and 110, respectively. In the maskingprocessing circuit 150, VIDEOs Y, M and C undergo color modification tobe suited for printing, and the color-modified VIDEOs Y, M and C arethen sent to the UCR processing circuit 160 by way of the signal lines111, 112, and 113, respectively. Based on the color modified signals Y,M and C, the quantity of BK (black) is determined in the UCR processingcircuit 160, after calculating the quantity of under colors to beeliminated. The BK reduced quantity of Y, M and C constitutes thecolor-modified quantity of Y, M and C.

These 4-color image signals Y, M, C and BK are then sent to the ditherprocessing circuit 170 through the signal line 114 in the order of Y, M,C and BK at each scan. The signal line 114 supplies the 6-bit digitalsignals. Based on these signals, the dither processing circuit 170digitally implements half tone representation in view of the dot densityper unit area. Dither processing is performed under three differentthreshold levels (explained later), and then 2-value signals are put outinto the signal lines 115-1, 115-2 and 115-3. In the multi-valueprocessing circuit 180, a 4-value pulse width modulation is implementedon the basis of the three 2-value signals 115-1, 115-2 and 115-3. The2-value signals having undergone pulse width modulation are sent to thelaser modulation unit 300 by way of the signal line 116. Then, laserbeams are released by the laser unit 320, which is driven by laserdriver 310 through line 311, thereby forming a latent image on thephotosensitive drum 24.

The sequence control of this apparatus as well as the control of eachprocessing unit are performed by the main unit controller 400.

Against the image data processing unit 100, the sequence controller411-65 (FIG. 3-1) within the main unit controller 400 sends out yellowexposure signals before manuscript exposure scanning to form the firstyellow toner image, magenta exposure signals before scanning to form thesecond magenta toner image, cyan signals to form the third image, andblack signals to form the fourth image. These signals are carriedthrough the signal lines 403, 404 and 406 shown in FIG. 4. The exposurelamps 5, 6 irradiate the white calibration plate 4 when exposurescanning for each color starts. At that time, the exposure start signal(shading start signal) 402 is sent out to the shading correction circuit130. After receiving this signal, the shading correction circuit 130reads the image data for correction corresponding to the whitecalibration plate to implement the shading correction, as explained indetail later.

FIG. 5-1 illustrates the construction of the synchronous control circuit190 which has been shown in FIG. 4. The synchronous control circuitconsists of the crystal oscillator 190-1, CCD read timing generator190-2, and address control unit 190-3. Synchronizing with the beamdetect signal BD 321-1 per one-line scanning from the laser scanner, thesynchronous control circuit drives the CCD and counts the serial pictureelement data released from the CCD and performs address control per eachscanning line.

The clock CLK 190 4, whose frequency is 4 times as high as the imagetransmission clocks 2φ T 190-9 and 190-12, is fed from the crystaloscillator 190-1 to the CCD read timing generator 190-2 and addresscontrol unit 190-3. The serial image data released from the CCD istransmitted by the image transmission clock 2φ T 190-9 to the CCDdrivers B-240, G-250 and R-260 via signal lines 102, 103 and 104,respectively. The image transmission clock 2φ T 190-12 sends data toeach processing circuit of the image processing unit 100 via signallines 101, 119, 120, 121, 118 and 117 (FIG. 4).

Synchronizing with the beam detect signal BD 321-1, the address controlunit 190-3 produces the horizontal synchronizing signals HSYNC 190-5 and190-11. By means of these synchronizing signals, the CCD read timinggenerator 190-2 sends out the shift pulse SH 190-6 (a signal that startsthe reading of CCDs B-210, G-220 and R-230) to the CCD drivers B-240,G-250 and R-260 via signal lines 102, 103 and 104, respectively, therebystarting the one-line output.

The φ-1 190-7, φ2 190-8 and RS 190-10 are the signals needed for CCDdriving. The CCD read timing generator 190-2 feeds these signals to theCCD drivers B-240, G-250 and R-260 via signal lines 102, 103 and 104,respectively. These signals will be discussed later.

The address line ADR 101-1 is a 13-bit signal line that counts the imagesignal of 4752 bits released from the CCD per each scanning line. Thisimage signal is sent to the shading correction circuit 130 by way of thesignal line 101. The shading start signal SHDST 401 is a signal thatruns from the main unit controller 400 into the address control unit190-3 and rises when the exposure lamps 5, 6 are scanning the whitecalibration plate 4 (FIG. 1). This signal becomes active when thehalogen lamps (for original lighting) 5 and 6 are turned on and theoptical system is positioned at the white calibration plate 4.

In that instance, the address control unit 190-3 sends out the signalSWE 101-2 to the shading correction circuit 130 via signal line 101, butthat applies to only the block where the one-line image data for thewhite calibration plate are released from the CCD. Signal CCD VIDEO EN117 indicates the block where 4752 bits of data are released from theCCD per each scanning line. This signal is sent to the multi-valuationprocessing circuit 180 by way of the signal line 117.

FIG. 5-2 shows a timing chart that indicates the timing pertaining toeach part of the synchronous control circuit 190. The signal 2φ Tindicates the image transmission clock which generates the one-clockhorizontal synchronizing signal HSYNC by synchronizing the beam detectsignal BD (which is released from the laser scanner per each scannerline) with the image transmission clock 2φ T. HSYNC is also the shiftpulse SH which starts CCD reading. The signals φ1 and φ2 indicate thesignals whose phase differs from each other and whose frequency isone-half the frequency of the image transmission clock 2φ T. Each ofthese signals constitutes a clock pulse which shifts the analog shiftregister pertaining to the even and uneven numbers of CCD.

VIDEO DATA is the image data signal from CCD, where the first image dataD1 are read from the output of shift pulse SH, leading successively toD2, D3, . . . and 4756 bits. D1 to D4 are the dummy picture elements ofCCD, whereas the 4752 bits from D5 to D4756 constitute the one-lineimage data, and the CCD VIDEO EN becomes active during this 4756-bitsection. The signal RS, produced at the trailing edge of image data, isthe pulse that resets the CCD shift register per shift. The shadingstart signal SHDST is a signal coming in from the main unit controller400 of this apparatus, but it rises only from the first active line ofCCD VIDEO EN.

Explanation of the CCD light-receiving unit 200, shown in FIG. 4, isdetailed as follows. The CCD light receiving unit 200 is made up of: thecolor separating prism 12 for 3-color separation; blue filter 13 forregulating the light intensity of B, G and R available from the colorseparating prism 12; green filter 15; red filter 17; CCD B-210 whichreceives the blue light; CCD G-220 which receives the green light; CCDR-230 which receives the red light; and CCD drivers B-240, G-250 andR-260 which digitize the analog valves of the complementary colorsY(yellow), C(cyan) and M(magenta) into digital guantity through A/Dconversion of the output from the above devices. CCDs B 210, G 220 andR-230 are incorporated in CCD drivers B-240, G-250 and R-260,respectively.

FIG. 6-1 shows the construction of each CCD. After passing through theinfrared cut filter, color separating prism 12, and spectral correctionfilter, the original image is irradiated in the form of a slit image onthe photodiode ranging between D1 and D5036. The photocurrent of thephotodiode is stored in the charge storage unit (not illustrated) in theform of an electric charge which is proportionate to the irradiationtime. This electric charge is shifted to the CCD analog shift registers1 and 2, with the shift pulse SH being added. The CCD shift registers 1and 2 receive a continuous pulse which has an antiphase consisting ofMOS φ1 and φ2. The electric charge of the image, shifted from the chargestorage unit of the photodiode, is transmitted in series to the outputtransistor circuit Q1, by means of the above clock pulse MOS φ1 and φ2,along the well of electric charge formed within the channel comprisingthe CCD shift registers 1 and 2.

Concurrently, a switching noise component produced by the reset signalRS, which corresponds to the above electric charge of the image, issupplied for the output transistor circuit Q2. Later, this switchingnoise component will be used to remove another switching noise componentincorporated into the image electric charge. The image electric charge,which has been transmitted to the output transistor circuit Q1 by meansof clock pulse MOS φ1 and φ2, is converted into the image voltage outputVS at this point. The switching noise component corresponding to this isalso converted into the switching noise voltage output VNS by means ofthe output transistor circuit Q2. In addition, every time an imagecharge undergoes voltage conversion after reading the output transistorcircuit Q1, another reset pulse MOS RS is sent to the output transistorcircuits Q1 and Q2, thereby preventing the image charge fromaccumulating in the output transistor circuit Q1.

FIG. 6-2 shows a block diagram of the CCD driver which converts theoriginal image (a practical example of this invention) into an electricsignal. Reference numeral 201 indicates the color separating prism 12and CCD linear image sensor IM SENS by which the image light passingthrough a light intensity adjust filter is converted into an electricsignal. Reference numeral 202 indicates the differential input videoamplifier V-AMP which provides differential amplification for the imagevoltage output VS and switching noise voltage output VNS (both arereleased from the IM SENS 201), thereby preparing a correct image outputvoltage VIDEO. Reference numeral 203 indicates the video A/D converter,A/D-C, which converts the image output voltage VIDEO from an analog intoa digital signal. Reference numeral 204 indicates the basic voltagesource V-REF which supplies basic conversion voltage for the A/Dconverter 203 above. Reference numerals 205 to 208 indicate the pulsedrive amplifiers which drive the IM SENS 201 to operate. Referencenumeral 209 indicates the variable resistance VR2 which eliminates theDC voltage difference between the image voltage output VS (the output ofIM SENS) and switching noise output VNS. Reference numeral 210 indicatesthe variable resistance VR1 which establishes the amplifying output ofV-AMP.

In the circuits mentioned above, the image output VS and noise outputVNS (released from IM SENS 201) are added to V-AMP 202 after their DCvoltage level is equalized by VR2 at the time of a non light signal.Both VS and VNS are differentially amplified by V AMP 202, through VR1210, thereby attenuating the noise component contained in VS whichimproves the image signal VIDEO so that it is suitable for processing byA/D-C 203.

In this embodiment, a simultaneous 3-color separation is implemented bythe color separating prism 12, as discussed before. However, due to thecharacteristics of the light source and color separating prism 12, andbecause of the color sensitivity of a CCD linear image sensor within theCCD driver, the light input and output signals of the three CCD driversB-240, G-250, and R-260 against B, G and R are adjusted by V-AMP 202 toprecisely harmonize the output signals with the non-light conditionswithout becoming saturated when receiving the maximum quantity of light.They are also adjusted to have a proper dynamic range so that their gainis reduced in the order of B, G and R by selecting the resistance (VR1and VR2) against B, G and R.

Conversion of the VIDEO signal from analog to digital is performed byA/D-C 203. The timing pertaining to conversion is subject to the imagetransmission clock 2φ T sent from the address control unit 190-3. Thedigitized VIDEO signal is then transmitted to the image data processingunit 100, where it implements the various steps of image processing.

The characteristics of the light source and other factors can becorrected by adjusting the gain of the amplifier according to the theabove mentioned method, i.e., in the form of B>G>R.

In this embodiment, the basic voltage such as REF, 3/4 REF, 1/2 REF, and1/4 REF is impressed in the high speed A/D converter A/D-C 203 at theoutput resistance whose level is lower than the basic voltage sourceV-REF 204. This is advantageous because it enhances linearity in theprocess of high-speed A/D conversion. Signals φ1, φ2 RS and SH, sentfrom the image data processing unit 100, are received by IM SENS 201 asa drive input after these signals are modified into proper drive voltagewaveforms such as MOS φ1, MOS φ2, MOSRS, and MOSSH by means of the pulsedrive amplifiers 205 to 208.

SHADING CORRECTION

FIG. 7-1 diagrams the shading correction practiced in this example. Theso-called "shading" implies an uneven optical image caused by variousoptical problems involving the light source, lens, and other factors.This occurs in the apparatus which reads out an image by applying alight source on an original and condensing its reflected image by lens.If the image data in the main scanning direction feature the valuesof 1. 2, . . . n . . . 4756 in FIG. 7-1, the quantity of light tends tobe attenuated at both ends.

To implement shading correction, the following measures are devised inthe case of the shading correction circuit 130. In FIG. 7-1, the legendMAX indicates the maximum value of image level, Sn indicates the imagelevel at the nth bit when reading the white calibration plate 4, and Dnrepresents the image level at the time of continuous image reading. Whenimplementing correction per bit, the corrected image level D'n can beexpressed by the following equation:

    D'n=Dn * MAX/Sn                                            (4-1)

FIG. 7-2 is a detailed diagram of the shading correction circuit 130.Reference numerals 130 2, 130-4 and 130-6 indicate the shading RAM forone-line reading of the white calibration plate 4. Reference numerals130-1, 130-3 and 130-5 indicate the shading correction ROM for providingcorrection output with reference to the shading data which have beenstored in the shading RAM at the time of image reading.

The 8-bit image data from CCD drivers B 240, G 250 and R-260 are fed tothe shading correction circuit 130 via signal lines 271, 272 and 273,respectively. First, the image data available from a one line reading ofthe white calibration plate 4 are stored in the shading RAMs 130-2,130-4 and 130-6. At that time, the shading light enable signal SWE isfed to the signal line 101-2 from the address control unit 190-3 (FIG.5-1). The image transmission clock 2φ T is also input to the signal line190-12, which is gated by the NAND gate 130-20. The output of the NANDgate 130 20 is connected via lines 130-16 through 130-19 to the lightenable terminal WE/ of the shading RAMs 130 2, 130-4, and 130-6. Theshading data can be accommodated by these RAMs only when a one-linereading of the white calibration is practiced in that instance, theaddress signal ADR 101-1 is controlled by the address control unit190-3, and each shading RAM is designed to accommodate the image data of4752 picture elements from the CCD output.

Image signals VIDEO Y, VIDEO M, and VIDEO C are output from the CCDlight-receiving unit 200 to the signal lines 271, 272, and 273,respectively. Each of these signals is an 8-bit digital signal to becalled "VIDEO 0 to 7" (from LSB to MSB) for each bit. When the shadingdata in this practiced example are accommodated in the shading RAMs130-2, 130-4, and 130-6, it is only the 6-bit digital data VIDEO 1 to 6that are memorized in each RAM as shading data per each picture elementby way of the signal lines 130-8, 130-10, and 130-12. The reasons why6-bit shading data have been adopted are that it reduces memory capacityand there is no radical fluctuation in shading characteristics.

When original scanning starts after accommodation of the shading data,the 8-bit data VIDEO 0 to 7 of the image data VIDEO Y, M, and C areinput to the address terminals A0 to A7 of the shading correction ROMs130-1. 130-3, and 130-5 via signal lines 130-7, 130-9, and 130-11. The4752-bit shading data, stored in the shading RAMs 130-2, 130-4, and130-6, are controlled by the address signal ADR 101-1, via lines 130-13,130-14, 130-15, and the shading data from each of the shading RAMs 1302, 130 4, and 130 6 is output to the address terminals A8 to A13 of theshading correction ROMs 130-1, 130-3, and 130-5 respectively, viaterminals I/01 to I/06 for each of the shading RAMs, respectively. Theshading light enable signal SWE 101-2 does not become active at thistime, whereas the shading correction RAMs 130-2, 130-4, and 130-6perform a lead action.

In the shading correction ROMs 130-1, 130-3 and 130-5, the ROM data areprepared so that an operation similar to the (4-1) equation, givenabove, shall be implemented. Access to the shading correction ROM isavailable if the 8-bit image signals VIDEO 0 to 7 and 6 bit shading datawork as an address. The shading-corrected output can thereby be outputfrom the terminals 01 to 08 in the form of an 8-bit image signal.

Shading correction shall be practiced for each scan of the original whenthe mode of multi-color superposition is employed.

This method of shading correction applies to all image data.

Υ CORRECTION

Explanation of the Υ correction will now be provided. FIG. 8-1 is adetailed block circuit diagram of the Υ correction circuit 140. Thispracticed example, in which the Y correction is implemented by means ofthe reference ROM for each color, features a construction where thecharacteristics can be selected optionally.

The 8 bit signal VIDEO Y, output from the shading correction circuit130, is synchronized by the synchronizing signal 2φ T which is put outon signal line 119 of the synchronous control circuit 190 to the latch301. The synchronized output is fed to the lower 8-bit address of the Υcorrection ROM 302. The upper 2-bit address receives the input of Υcorrection select signal 403 sent from the control unit 400. The area ofΥ correction ROM 302 is selected according to the select signal 403.

The Υ-value control switch 421-14 for Y (yellow) (FIG. 3--3) of thesub-control unit 421 (located within the main unit controller 400) iscapable of being selected under four categories. This switch givesaccess to the high-speed digital signal which is fed to the upper 2-bitand lower 8-bit address of the Y correction ROM 302. The data previouslymemorized in the ROM 302 can thereby be released. Therefore, the datafrom the ROM feature a 6-bit level. These data are further synchronizedby the synchronizing signal 2φ T which is ouput to signal line 119 fromthe synchronous control circuit to the latch 303. The signal VIDEO Y isthen output to the signal line 108 after going through Y correction inthe masking processing circuit 150. Data conversion of the yellow (Y)signal component is thus accomplished by the Υ correction ROM 302.

The image signals VIDEO M and C undergo similar steps of processing.After being sent out from the shading circuit 130 to the signal lines106 and 107, the image signals VIDEO M and C go through synchronizationat the latches 304 and 307 and enter the Υ correction ROMs 305 and 308.Access to the area of the Υ correction ROMs 305 and 308 is subject tothe image signals VIDEO M and C as well as to the selection signalscontrolled by the Υ value control switches 421-15 and 421-16 (FIG. 3-3)of the sub-control unit 421 which is located within the main unitcontroller 400. Output of the 6-bit Υ corrected data are implementedthrough this access. These Υ corrected signals VIDEO M and C undergosynchronization in the latch circuits 306 and 309 and then come out tothe masking circuit 150 via signal lines 109 and 110.

Next explanation is concerned with: how to select the Υ value controlswitches 421-14 to 421-16 which belong to the sub-control unit 421 ofthe main unit controller 400; and conversion table for the address inputand output data pertaining to the Υ correction ROMs 302, 305 and 308. Inthis case, the Υ correction ROM 302 of the image signal VIDEO Y providesan example for the explanation.

When implementing Υ correction, it is advisable establish a ratio of 1to 1 between "OD" (density of a color original based on reading) and"CD" (density of a transfer paper based on depicting). In that case,there are three major factors (properties) that affect Υ correction:properties of the CCD B 210 which reads the density of a color original;properties of the image processing unit 100 by which the signal from CCDis released in the form of laser-modulated signal; and density of theimage depicted on a transfer paper by means of the laser-modulatedsignal. More detailed explanation is given to these factors by referenceto FIG. 8-2.

In the fourth quadrant of FIG. 8-2, the axis of ordinates represents OD,while that of abscissas stands for the shading-corrected VIDEO Y. SinceOD is given in logarithm, the image signal VIDEO Y features alogarithmic relation with the original density OD. This relation becomesfixed depending on the properties of CCD B 210 and CCD driver 240.

The second quadrant represents the relationship between CD anddither-accumulated frequency number. The dither accumulated frequencynumber implies the ratio between a certain entire area (in this case itindicates the dither matrix represented by the dither processing circuit170 to be discussed later) and an inner partial area under development.The change of CD is subject to the change of the dither accumulatedfrequency number which ranges from 0 to 100 percent. At 0%, the CDremains white but as the dither accumulated frequency number enlargesgradually, the CD begins to show a sharp increase halfway, andultimately, i.e., at 100% the CD becomes saturated at a certain degreeof density. These tendencies become fixed depending on the properties ofthe photosensitive drum 24, yellow developer 36, and other devices.Accordingly, the relation between CD and OD becomes established in thethird quadrant, if the characteristics of the image processing unit 100are incapable of being changed in the first quadrant.

In the image processing unit 100, the relation between CCD output anddither-accumulated frequency number can be controlled particularly bythe Υ correction circuit 140 and dither processing circuit 170. However,the data handled by the dither processing circuit are the 6-bit data (asexplained later), and therefore the quantum error enlarges if the nonlinear segment of the second and fourth quadrants is corrected. This isone of the shortcomings because the relation between CD and OD cannot beshown accurately even if the linearity is achieved.

The input and output data of the Υ correction circuit 140 are 8-bit and6-bit respectively, and therefore the quantum error diminishes in spiteof correction. In the dither processing circuit 170, the characteristicspertaining to the first quadrant become fixed depending on the datastored in the Υ correction ROM 302, if there is a linear correlationbetween the signals from the UCR processing circuit 160 and thosereleased as the dither-accumulated frequency number. Therefore, if therelation between CCD output and dither-accumulated frequency number inthe first guadrant acquires the characteristics of A through Υcorrection, then the relation between CD and OD in the third quadrantmay be established at the ratio of 1 to 1 like A'.

Details of the Υ correction ROM 302 are given in Table 1, which follows,as a practical example. Its characteristics are shown by the upper 2bits of address, where "00" indicates A, "01" B, "10" C, and "11" D.When the yellow image signal VIDEO Y is put in the lower 8 bits, the6-bit data will be put out as shown in Table 1. In this way it ispossible to achieve a 1 to 1 ratio between CD and OD. As in the case ofB' in the third quadrant, the characteristics of copy density such aslowering CD, highly contrasting C', slightly covering D', and so on, canalso be controlled by choosing the Υ correction switch 421-14 of thesub-control unit 421.

Quick and accurate copying is thus realized by implementing Υ correctionfor the characteristics of yellow signal. This also applies to magenta(M) and cyanogen (C) signals, whose characteristics are also subject tofree selection. T1 TABLE 1-? Lower 8-bit? ? -Upper 2 bit address?address? Data Output? - 00 00000000 000000 - 00000001 000010 - 00001110010001 - 00011010 010110 - 11111000 110000 - 11111110 111100 - 11111111111111 - 01 00000000 000000 - 00010000 000000 - 11111111 111111 -

The relation between CCD output and dither-accumulated frequency numberis also controllable by both the Υ correction circuit 140 and ditherprocessing circuit 170. Since there is no linear correlation between OD(density of original) and VIDEO Υ (signal released after shadingcorrection), it is necessary to implement signal conversion based on apreviously mentioned method so that OD becomes proportional to VIDEO Y,whose signal has been corrected by the Υ correction ROM 302. The ditherprocessing circuit 170, for which the Υ-corrected VIDEO signal has beensupplied via signal line 114, may also be corrected by the ditherprocessing circuit mentioned later so that the CD density becomesproportional to the VIDEO signal.

MASKING

Color materials such as toner, printing ink, etc. have the spectralreflection factor shown in FIG. 9-1. The yellow (Y) color materialabsorbs the light of 400 to 500 nm and reflects that of 500 nm or more.The magenta (M) color material absorbs the light of 500 to 600 nm andreflects others, while the cyan (C) color material absorbs the light of600 to 700 nm and reflects others.

When performing development with the Y color material, it is necessaryto perform it on a latent image formed through the optical image inwhich the light reflected from the original is color separated by a blue(B) filter featuring the spectral transmission factor shown in FIGS.2-4. Likewise, it is necessary to use green (G) and red (R) filters fordevelopment with the M and C color materials, respectively.

As is evident from both figures, each of the filters B, G and R featuresa relatively good separation of color components above 500 to 600 nm,whereas the spectral reflection factor of color materials shows a badseparation depending on wavelength. M (magenta), in particular, containsa sizable guantity of Y (yellow) and C (cyan) components. C alsocontains a little M and Y components. Conseguently, a copied colorpicture tends to become turbid as it involves unnecessary colorcomponents, if development is performed with the above color materialsbased on an optical image which has undergone simple color separation.

In ordinary printing technology, therefore, a masking processing methodis employed to make up for these drawbacks. In the masking processingsystem, the output color components Yo, Mo and Co are expressed by thefollowing formulas, with Yi, Mi and Ci representing the input colorcomponents: ##EQU1## These lead to the following formulas, therebyimplementing conversion:

    Yo=a.sub.1 a.sub.1 Yi-b.sub.1 Mi-c.sub.1 Ci                (3)

    Mo=-1.sub.2 Yi+b.sub.2 Mi-c.sub.2 Ci                       (4)

    Co=-a.sub.3 Yi-b.sub.3 Mi+c.sub.3 Ci                       (5)

Turbidity of a picture can be corrected by applying relevantcoefficients (ai, bi, ci) (i=1, 2, 3) to the above formulas.

FIG. 10-1 is a detailed diagram of the masking processing circuit 150and UCR processing circuit 160. In this figure, 150-Y, 150-M and 150-Cindicate the masking processing units corresponding to the image signalsY (yellow), M (magenta), and C (cyan).

In the masking processing unit 150-Y, the formula (3) above is realizedby Yi, Mi and Ci, each of which corresponds to: the 6-bit Y-componentvideo signal VIDEO Y released via signal line 108; upper 4 bits of the6-bit M-component video signal VIDEO M released via signal line 109;upper 4 bits of the 6-bit C-component video signal VIDEO C released viasignal line 110. Mi and Ci in the formula (3), Yi and Ci in the formula(4), and Yi and Mi in the formula (5) are the color data for correcting.These color data for correcting do not require higher accuracy than thecolor data for being corrected (Yi, Mi and Ci). The coefficients (ai,bi) (i=1, 2, 3), which range over 16 steps (1/16, 2/16 . . . 1) asexplained later, are reduced to 4 bits against 6 bits of the data forbeing corrected (Yi, Mi and Ci). The capacity of ROM for conversion canthereby be reduced to 1/4.

FIG. 9-2 is a detailed block circuit diagram pertaining to the maskingprocessing unit 150-Y in FIG. 10-1. Explanation of the maskingprocessing units 150-M and 150-C is omitted since they feature the samecircuit as above.

By means of the digital code switches 421-5 to 421-13 located over thesub-control unit 421 (FIG. 3--3), the following data are sent into themasking processing unit shown in FIG. 9-2. The 6-bit data Y via signalline 150-10; 4-bit data M via signal line 150 12; 4-bit data C viasignal line 150 14; and 4-bit code data S-YY, S-YM and S-YC establishedby users via signal lines 150-11, 150-13 and 150-15. Based on theformula (3) with coefficients ai, bi and ci, the coefficient of the codedata S-YY, S-YM and S-YC ([O]_(H) ˜[F]_(H)) turns out N/16, with thevalue of digital code switches 421-5 to 421-13 being set at N.

Numbers 150 1, 150-2 and 150-3 indicate the ROMs to be used foroperation. 150-1 stands for the 6-bit signal Y. The 4-bit code data S-YYforms the address for each ROM. With the ROM data being defined by thataddress and the 4-bit value being set at m, the data expressed by thefollowing equation are accommodated in 6 bits:

    D.sub.y =Y.sub.6 bit×m/16 (Y=O.sub.H ˜3F.sub.H, m=O.sub.H ˜F.sub.H)

Under the set value n and 4 bit code data S-YM, the following equationapplies to 150-2:

    D.sub.m =M.sub.4 bit×n/16

Under the set value 1, the following equation applies to 150-3:

    D.sub.c =C.sub.4 bit×1/16

Both D_(m) and D_(c) represent 4-bit data in the above equations. Thedata Dy, Dm and Dc, available from the above equations, will be sent tothe signal lines 150-16, 150-17 and 150-18 respectively. Application ofthese data to the formula (3) brings the following equation:

    D=D.sub.y -D.sub.m -D.sub.c

If the value found from the above equation constitutes the video datafor Y, the correction of Y can be implemented by applying the formula(1). The 6-bit data Y and 4-bit correction data M and C are connected tothe address path of the operation ROM 150-4, thereby providing aprescribed operation value for ROM table reference. 150-5 indicates alatch element that synchronizes with the video transmission clock 2φ Tto latch the 6-bit data which have undergone numerical operation formasking processing. Correction of M and C is similarly implemented in150-M and 150-C.

UCR PROCESSING

FIG. 10-1 shows the details of the UCR processing circuit. Equalquantities of Y, M and C, for example, may be superposed in the case ofcolor reproduction by mixing color materials based on the subtractivemixture method. In that case, the color materials being used absorb allspectral components being separated, thereby reproducing the black (BK)color. In the BK area of the original, therefore, the toner of Y, M andC overlaps in equal quantities.

However, the spectral reflection factor applying to the toner of Y, Mand C features deficient color separation caused by wavelength, asevident from FIG. 9-1. As mentioned already, the Y toner contains alittle M component and the M toner contains a sizable guantity of Y andC components. Therefore, color reproduction for the BK component must beperformed by means of the BK toner. In the area where BK is applied, itsuffices to reduce the guantity of toners correspondinq to Y, M and C.This method is called UCR (elimination of under colors), which isimplemented in the block 160 of FIG. 10-1.

The 6-bit image data for Y, M and C are released from the maskingcircuit 150 by way of the signal lines 160-30, 160-31 and 160-32. Thesedata first undergo large-small comparison between Y and M, M and C, andC and Y by means of the comparators 160-1, 160-2 and 160-3,respectively. The large-or-small comparison by these comparators isintended to latch the smallest value among the image data Y, M and C inthe latch circuits 160 13, 160 14 and 160 15.

Depending on the size of those image data, the signals as shown in thetable of FIG. 10-2 will be sent out the signal lines 160-33, 160-34 and160-35. Upon comparison of the image data Y, M and C per pictureelement, "0" will be released to the signal line 160-33 and "1" to160-35, when Y is the smallest. The signal lines 160-33 and 160-35 areconnected to a logic circuit, which includes a logic inverter 160-5 anda logic NAND 160-4, that outputs a latch enable signal L_(y). When Y isa minimum, latch enable signal L_(y) enables the latch 160-13 to latchthe image data Y.

Likewise, "1" will be released to the signal line 160-33 and "0" to160-34, when M is the smallest. The signal lines 160-34 and 160-33 arealso connected to a logic circuit, which includes a logic inverter 160-7and a logic NAND 160-6, that outputs a latch enable signal L_(m). Thelatch enable signal L_(m) enables the latch 160-14 to latch the imagedata M if M is a minimum. "1" will be released to the signal line 160-34and "0" to 160-35, when C is the smallest. The signal lines 160-35 and160-34 are connected to a logic circuit, which includes a logic inverter160-9 and a logic NAND 160-8, that outputs a latch enable signal L_(m).If C is a minimum, the latch enable signal L_(c) enables the latch160-15 to latch the image data C. When Y, M and C are all equal to eachother (Y=M=C), the value of Y shall represent them all.

The smallest value, established by the above three comparators, is putout to the signal line 160-36 through the latch circuits 160-13, 160-14,and 160-15, and thereafter it constitutes the basic data for black inksupply. Image data Y, M, and C, released from the masking circuit 150are latched by other latch circuits 160-10, 160-11, and 160-12 at theleading edge of the image transmission clock 2φ T, and then output tothe subtractive operation ROMs 160-16, 160-17, and 160-18 at the nextstage. By means of the multiplication ROM 160-19, the above basic data(BK) for ink supply which have been put out to the signal line 160-36are multiplied by the 4-bit coefficients fed to the signal line 160-37through the selector 160-20. The upper 4 bits of the 6-bit values(K×BK), resulting from this multiplication, are output to thesubtraction ROMs 160-16, 160-17, and 160-18 by way of the signal line160-38. The subtraction ROMs 160-16, 160-17, and 160-18 subtract thesevalues from each of the image data and send out the results to theselector 160-21 by way of the signal line 160-39. The selector 160-21takes in the 6-bit ink supply data from the multiplication ROM 160-19through the signal line 160-38.

These image signals are released from the selector 160-21 in the form of6-bit signals after the required image data are selected by thediscrimination signals SEL BK (where SL corresponds to SEL BK) Y, SEL M,and SEL C (which discriminate Y, M, C and BK) which are sent from themain unit controller 400 through the signal lines 405 1, 405 2, 405-3,and 405-4. In the case of full-color mode involving four colors (Y, M, Cand BK), the final output, having undergone the masking and UCRprocessing, goes through the selection signals SEL Y, SEL M, SEL C, andSEL BK per scan, which select the image data whose color has beenmodified in the order of Y, M, C, and BK.

The coefficients to be multiplied by the basic data of BK are selectedby a series of switches 421-1 to 421-4 which are located within the subcontrol unit 421 of the main unit controller 400 shown in FIG. 3-3.These coefficients are fed to the multiplication ROM 160-19 after beingselected in a similar way by the selection signals SL 405-9 and SL405-10 of the above switches released from the system control unit.

In the UCR circuit 160 of this practiced example, as explained before,the black ink supply is implemented on the basis of the value BK whichhas been found through multiplication of the coefficient k by thesmallest value (Y, for example) of the picture elements containing acolor component as shown in FIG. 10-3. The ultimate color components ofY, M, and C, resulting from operation, are (Y - BK), (M - BK), and (C -BK) respectively.

MULTI-GRADATION

FIGS. 11A and 11B diagram the multi-gradation processing of thispracticed example. The multi-gradation processing in this practicedexample is made up of dither and multi-value processings. An example ofdither processing is given in FIG. 11A. In dither processing, the2-value version of the 6-bit and 64-level (0 to 3F) digital imagesignals is brought by changing the threshold in a certain area, therebyachieving the gradation based on an areal ratio of the dot number withinthat area (hereinafter referred to as "dither matrix").

In FIG. 11A-A, the threshold is changed from 8 to 18, 28, and 38 per bitin a 2×2 dither matrix. Against the values 0 to 3F of the digital imagesignal Dn, five different gradations are attained as shown in A-(0) toA-(4) of FIG. 11A, with "0" standing for the white block and "1" for theblock with oblique lines according to 2-value signals.

The larger the dither matrix, the greater the gradation number, butpictorial resolution declines to the contrary. In this invention,therefore, the gradient features are enhanced through pulse widthmodulation, with a picture element being further divided. FIG. 11B showsan example where 4-value dither is implemented through 3-divisionalpulse width modulation. Here, a dot is divided into three parts ormicropixells by a perforated line, as illustrated in the figure. That isto say, an areal ratio consisting of four gradations is available perdot. As illustrated in FIG. 11B-B, 13 gradations B-(0) to B-(12) areachieved by giving three more threshold levels to each dot of the 2×2dither matrix.

In the 2-value signal under multi-gradation, therefore, a picture ofgood gradating characteristics is realized by emitting laser light toonly the blocks with oblique lines as shown in FIG. 11B. In the case of3-value dither matrix, a matrix is produced by dividing a dot into twoparts or micropixels. As for this practiced example, the dither matrixis variable from 2×2 to 32×32, where multi-value performance may bechosen from among 2-value, 3-value, and 4-value steps by means of theswitch 421-24 (FIG. 3-3) in the sub-control unit 421. A variety ofgradation can be achieved through combination of these steps. Moire andother factors can also be reduced by altering the dither matrix for eachcolor.

FIGS. 12-1 and 12-2 are the detailed block circuit diagrams illustratingthe dither processing circuit 170 and multi-value processing circuit180. Colors that require dither processing are determined by the 2-bitsignals YMC BK-0 (A10) and YMC BK-1 (A11) which are sent from the mainunit controller 400 via signal line 406 (FIG. 4). Examples are givenbelow.

    ______________________________________                                        Y (yellow)   in case of                                                                             A10 = 1 and A11 = 1                                     M (magenta)  in case of                                                                             A10 = 1 and A11 = 0                                     C (cyanogen) in case of                                                                             A10 = 0 and A11 = 1                                     BK (black)   in case of                                                                             A10 = 0 and A11 = 0                                     ______________________________________                                    

Switches SW 1 to 3 are intended to select gradating characteristics andthere are two contacts (a and b) in these switches. A dot of the dithermatrix can be divided into three segments by turning on the switch SW 1.A dot of the dither matrix can be divided into two segments by turningon the switch SW 2.

As an example, there is a case featuring: A10=1; A11=1; SW 1 on; SW 2off; and SW3 off. The dither ROMs A to C will be selected in this case.(Similarly, if SW 2 is on then dither ROM D 170-12 and dither ROM E170-13 are selected; and if SW 3 is on, then dither ROM F 170-14 isselected). Under the conditions where 6-bit (64-level) video signal isapplied, the following dither patterns shall be stored in the address ofeach dither ROM. Dither ROM A 170-9: 00 in address 00, 03 in 01, 06 in02, 09 in 03, 12 in 20, 15 in 21, and so on. Dither ROM B 170-10: 01 inaddress 00, 04 in 01, 07 in 02 and so on. Dither ROM C 170-11: 02 inaddress 00, 05 in 01, 08 in 02, and so on. Instead of performingcomparison between the threshold of image data and dither pattern bystoring dither patterns in each dither ROM, there is another ditherprocessing method where dither converted data are stored in a memorybeforehand, and access is given to that memory, with the input imagedata functioning as address.

Circuit operation under the above conditions is explained as follows.

When the video signals VIDEO 0 to 5 indicate 04 under these conditions,the output Q of latch A is "1" since the video signals are greater ifcompared, using comparator 170-1, with the content 00 at the address 00of the dither ROM A. The output Q of latch B is also "1" since videosignals are greater, as determined by comparator 170-2, than the content01 at the address 00 of the dither ROM B. The output Q of latch C isalso "1" since video signals are greater, as determined by comparator170-3, than the situation 02 at the address 00 of the dither ROM C.

The output Q of latch A is "1" as compared with the situation 03 at theaddress 01 of the dither ROM A because the video signals synchronizewith the next image transmission clock WCLK. The output Q of latch B is"0" because the video signals are egual to the situation 04 at theaddress 01 of the dither ROM B. The output Q of latch C is "0" ascompared with the situation 05 at the address 01 of the dither ROM C.

In this way, the output Q of the latches A, B, and C becomes "0" or "1"depending on the results of comparison, as determined by comparators170-1, 170-2, and 170-3, with the situations at the addresses 02, 03,00, 01, 02, 03, and 00 of each of the dither ROMs A, B, and C insynchronization with WCLK. If the signal HSYNC comes in at that time,the address counter B 170-8 counts up one, causing synchronization withWCLK, and then comparison with the situation is performed successivelyat the addresses 20, 21, 22, 23, and 20. That is to say, undersynchronization with the image transmission clock WCLK, the addresscounter B 170-8 (upper address) (0 x address-3 x address) counts upevery time the address counter A 170-7 (lower address) (x 0 address-x 3address) counts up and HSYNC comes in.

In that instance, the output of the latches A 170-4, B 170-5, and C170-6 is stored in the line memories A 180-9, B 180-10, and C 180-11respectively because the address of the line address counter C 180-7counts up under synchronization with the image transmission clock WCLK.If the signal HSYNC comes in at that time, the output of the latches A170-4, B 170-5, and C 170-6 is stored in the line memories D 180-12, E180-13, and F 180-14, respectively, because the address of the lineaddress counter D 180-8 counts up under synchronization with WCLK. Whilebeing stored successively in the line memories D 180-12, E 180-13, and F180-14 in synchronization with WCLK, the content previously stored inthe line memories A 180-9, B 180-10, and C 180-11 is sent successivelyto the data selector 180-15 because the address of the line addresscounter C 180-7 and lead address counter 180-5 counts up insynchronization with the signal RCLK released from the oscillationcircuit 180-3.

In order to form an image on a fixed spot over the drum, it isnecessary, in the above conditions, to delay the start of imageformation for a certain length of time after the input of HSYNC addresscounter 180-5 is prohibited until this delay reaches the time equal tothe value established by the left margin counter 180-6. In other words,the information stored in the line memories A, B, C or D, E, F can besent out to the data selector 180-15 only after the prohibitionterminates.

Each time the signal HSYNC comes in, the input of the data selector180-15 undergoes alternate changeover to A and B implemented by thechangeover circuit 180-2. Therefore, the output terminals of the dataselector 180-15 are always sending out the signal which, insynchronization with RCLK, has been stored in either of the linememories A 180-9, B 180-10, and C 180-11 or line memories D 180-12, E180-13, and F 180-14.

As illustrated in FIG. 13, the image transmission clock WCLK is dividedinto three signals φA, φB, and φC by the multi-value oscillation circuit180-16. The multi-value oscillation circuit 180-16 sends these threesignals to the AND gates A 180-17, B 180-18, and C 180-19 respectively,if its contact SW_(1-b) (400-6) is turned on. As a result, the outputsY0, Y1, and Y2 having synchronized with the RCLK of the data selector180-15 are gated at the AND gates A, B, and C respectively. This resultis then put in the OR gate 180-20, whose output signal turns on thelaser. Depending on the magnitude of the signals VIDEO 0 to 5 which havebeen fed into the comparator during the one wave of WCLK, the emissionof laser light can be varied under four different patterns: (1) notemitted at all; (2) emitted for one-third of the time of RCLK; (3)emitted for two thirds of the time of RCLK; and (4) emitted for a timeperiod RCLK.

The time chart pertaining to the above-mentioned signals is given inFIG. 13. Explanation of these signals runs as follows:

BD

Released every time the laser light scans over the drum.

HSYNC

Becomes H only while the first φ1 remains H after BD has become H.

VIDEO ENABLE

Only while this VIDEO ENABLE remains H, the video signaldither-processed at the line memory is stored in the line memory.

LASER OUTPUT

Only while this laser output remains H, the laser light modulated on thedrum is emitted.

IMAGE TRANSMISSION CLOCK (WCLK 2φ T)

Under synchronization with this WCLK, the dither-processed video signalis stored in the line memory.

φ1

Under synchronization with this φ1, a signal is taken out of the linememory.

φA, φB, φC

Under synchronization with φ1, the signal taken out of the line memoryis divided into three by these φA, φB and 100 C.

The following explanation concerns with the case where the area subjectto laser emission, during one wave of the image transmission clock WCLK,is varied under three different patterns. In this case, the switchesSW1, SW2, and SW3 are OFF, ON and OFF, respectively. Other conditionsare the same as in the case of SW1 ON, SW2 OFF, and SW3 OFF. Dither ROMsD 170-12 and E 170-13 are selected under these conditions.

The function of the right address counter 180-1, read address counter180-5, left margin counter 180-6, changeover circuit 180-2, line addresscounter C 180-7, and line address counter D 180-8 is the same as in thecase discussed before, and therefore explanation of these devices isomitted now.

The results of comparison between VIDEOs 0 to 5 and dither ROM D 170-12are sent into the terminal Ao (or Bo) of the data selector 180-15 by wayof the latch A 170-4 and line memory A 180-9 (or line memory D 180-12).Likewise, the results of comparison between VIDEOs 0 to 5 and dither ROME 170-13 are sent into the terminal A1 (or B1) of the data selector180-15 by way of the latch B 170-5 and line memory B 180-10 (or linememory E 180-13). When SW_(2-b) is On, the signal RCLK is divided intotwo signals 100 A and 100 B by the multi-value oscillation circuit180-16, as illustrated in FIG. 13, but 100 C remains 0 in the mean time.As a result, the outputs Y0 and Y1, synchronized with RCLK of the dataselector 180-15, are gated at the AND gates 180-17 and 180-18.

Then, logic OR operation is effected at the OR gate 180-20, and thelaser is turned on by this signal. Now, depending on the magnitude ofthe signals VIDEO 0 to 5 which have been fed into the comparator duringone wave of the image transmission clock WCLK, the emission of laserlight can be varied under three different patterns: (1) not emitted atall; (2) emitted for one-half of the time of RCLK; and (3) emitted for atime period RCLK.

The following explanation is concerned with the case where the areasubject to laser emission, during one wave of the image transmissionclock WCLK, is varied under two different patterns. In this case, theswitches SW1, SW2, and SW3 are OFF, OFF, and ON respectively. Otherconditions are the same as in the cases of SW1 ON, SW2 OFF, and SW3 OFF.Dither ROM F 170-14 is selected under these conditions. The function ofthe right address counter 180-1, read address counter 180-5, left margincounter 180-6, changeover circuit 180-2, line address counter C 180-7,line address counter D 180-8 is the same as in the case explainedbefore.

The results of comparison between VIDEOs 0 to 5 and dither ROM F 170-14are sent into the terminal Ao (or Bo) of the data selector 180-15 by wayof the latch A 170-4 and line memory A 180-9 (or line memory D 180-12).

In the multi-value oscillation circuit 180-16, on the other hand, 100 Ais "1", φB "0", and φC "0", all remaining unchanged when SW 3-b is ON.Therefore, Y0 synchronizes with RCLK and bypasses the AND gate 180-17.Next, logic OR operation is effected at the OR gate 116, and the laseris turned on by this signal. Now, laser goes on and off in accordancewith the magnitude of the signals VIDEO 0 to 5 which have been fed intothe comparator in one wave of WCLK.

The type of originals is roughly grouped into three categories: (1)pictures only; (2) letters only; and (3) both pictures and letters.Pictures are further divided into those such as photographs featuring adelicate tone of color and those such as comic strips and line drawings(for coloring) involving almost primary colors only. As for photographicoriginals, accurate reproduction of various delicate colors isrealizable through enhancement of gradation by multi-value processing.

As for comic strips and line drawings in which almost primary colorsalone are involved, clear and unclouded color reproduction is realizablethrough 2-value processing As for letter originals, distinct pictorialexpression free from half-tone density is practicable, therebyreproducing an optimal image through changeover of switches (SW 1 to 3)depending on the type of originals.

The on-off operation of the switches SW 1 to 3 is implemented throughchangeover of the switch 421-24 in the sub-control unit 421. SwitchesSW1, SW2, and SW3 are designed to be on at dials 4, 3, and 2 of theswitch 421-24.

The apparatus introduced in this practiced example is designed to recordimages by means of laser beams, but application is not confined to this.It is also applicable to thermal printers, ink jet printers, etc. Someitems of this invention are applicable to black and white imageprocessings, as well as color images.

Either of the masking or UCR processings may be implemented first. It isallowable to use the B, G, and R signals transmitted from the memoriesof a host computer. It is allowable to read out the Y, M, C, and BK dataafter they have been stored in the page memory. Images may be eitherrecorded on a transfer paper or filed in a disc. Multi-gradation isperformed by time division signals in this practiced example, but it mayalso be performed through luminance modulation.

What we claim is:
 1. An image signal binarizing process comprising thesteps of:inputting an image signal representative of an image; providinga threshold pattern formed by a plurality of pixels, each of said pixelscorresponding to a different pixel of the image represented by saidimage signal; dividing each pixel of said threshold pattern into aplurality of micropixels, each pixel having the same number ofmicropixels; setting a different threshold value for each of saidmicropixels; processing said image signal in accordance with saidthreshold values of said micropixels to produce a binary image signal;and selecting the number of micropixels in one pixel; wherein the sizeof said micropixels in each pixel is reduced as the number ofmicropixels increases.
 2. The process according to claim 1, wherein thearrangement of the micropixels in a pixel is the same arrangement forall pixels.
 3. The process according to claim 1, wherein said imagesignal is a color image signal having a plurality of color componentsignals.
 4. The process according to claim 3, wherein said thresholdpattern is different for respective color component signals.
 5. Ahalftone image recording apparatus comprising:means for recording animage on a recording medium; means for inputting an image signalrepresentative of an image which includes a plurality of density levels;periodic signal generating means for generating a plurality of types ofperiodic signals whose widths are different; means for combining atleast one periodic signal generated by said generating means with saidimage signal to form a combined signal; and means for applying saidcombined signal to said recording means.
 6. Apparatus according to claim5, wherein said recording means performs a recording by the use of alight beam and the light beam is modulated by said combined signal. 7.Apparatus according to claim 5, wherein said means for combiningincludes means for processing the image signal in accordance with athreshold pattern to produce a binary signal, the threshold patternbeing varied.
 8. Apparatus according to claim 5, wherein said imagesignal is a color image signal including a plurality of color componentsignals.
 9. A halftone image recording apparatus comprising:means forrecording an image on a recording medium; means for inputting an imagesignal representative of an image which includes a plurality of densitylevels; means for generating a periodical signal, said generating meansbeing able to generate a plurality of types of periodical signals whoseperiods are different from each other; means for forming a recordingsignal based on said periodical signal generated by said generatingmeans and said image signal; and means for applying said recordingsignal to said recording means.
 10. Apparatus according to claim 9,wherein said periodical signal is a periodical pulse signal. 11.Apparatus according to claim 9, wherein said recording means performs arecording by use of a light beam and the light beam is modulated by saidrecording signal.
 12. Apparatus according to claim 9, wherein saidforming means includes means for processing said image signal inaccordance with a threshold pattern signal to produce a binary signal,said pattern signal being varied by said generating means.
 13. Apparatusaccording to claim 9, wherein said inputting means includes a reader forconverting an image of an object into an image signal which includes aplurality of density levels.
 14. Apparatus according to claim 9, whereinsaid image signal is a color image signal having a plurality of colorcomponents and said generating means and said applying means execute thegenerating and applying operations for every color component of saidcolor image signal.
 15. Apparatus according to claim 9, furthercomprising means for manually selecting the type of the periodicalsignal generated by said generating means.
 16. Apparatus according toclaim 15, wherein said periodical signal is a periodical pulse signal.17. Apparatus according to claim 15, wherein said recording meansperforms recording by use of a light beam and the light beam ismodulated by said recording signal.
 18. A half-tone image recordingapparatus, comprising:image signal generation means for generating animage signal which represents an image including a half-tone image;combined signal formation means for forming a combined signal bycombining the image signal generated by said image signal generationmeans with a periodic signal selected from plural periodic signals, theplural periodic signals respectively having different periods; supplymeans for supplying the combined signal into a recording device; andchangeover means for changing between forming a combined signalcorresponding to a first periodic signal and forming a combined signalcorresponding to a second periodic signal, said changeover meanseffecting the change by selecting a different periodic signal from theplural periodic signals, the period of the first periodic signal beingdifferent from that of the second periodic signal.
 19. An apparatusaccording to claim 18, wherein said image signal generating meansgenerates the image signal by reading an objective image.
 20. Anapparatus according to claim 18, wherein said recording devicecomprises:a light generation device which is driven in response to thecombined signal; and a light sensitive body for receiving a lightgenerated by said light generation device.
 21. An apparatus according toclaim 18, wherein the periods of the first and second periodic signalscan be expressed substantially by an integer ratio.
 22. An apparatusaccording to claim 18, further comprising:set means for indicating achangeover state of said changeover means.
 23. An apparatus according toclaim 18, wherein said combined signal formation means further comprisesa table to which the image signal is input as an address and whichstores therein the combined signal.
 24. An apparatus according to claim20, further comprising:means for detecting the light from said lightgeneration device to generate a beam detector signal; and control meansfor controlling a recording timing of said recording device inaccordance with the beam detector signal.
 25. Apparatus according toclaim 5, wherein said combining means includes selection means forselecting at least one periodic signal with a selected width from amongsaid plurality of periodic signals.